Optical scanning apparatuses that vibrate an optical fiber for guiding light from a light source, such as a laser, and scan emitted light over an object in a spiral pattern have been proposed (for example, see JP 5190267 B2 (PTL 1) and JP 2014-147462 A (PTL 2)). In such optical scanning apparatuses, the tip of the optical fiber is supported at one end in a vibratable state and is driven in two axial directions, orthogonal to the optical axis of the optical fiber and orthogonal to each other, by a drive mechanism that uses piezoelectric elements or electromagnetic means. By shifting the phase of vibration in the two orthogonal axial directions by 90° from each other, vibrating at the same frequency, and causing the amplitude of vibration to rise and fall periodically between zero and the maximum, the object can be scanned over a spiral scanning pattern. Such a spiral scanning pattern is also referred to as a spiral scan.
The frequency producing vibration in the optical fiber of an optical scanning apparatus is often set near the resonance frequency of the tip of the optical fiber. The reason is that setting the driving frequency near the resonance frequency allows scanning at a larger amplitude with less energy. For example, PTL 2 discloses a method for using an optical position detector, such as a Position Sensitive Detector (PSD), to detect the scanning pattern of a spiral scan and for adjusting the driving parameters, such as the amplitude, phase difference, and driving frequency, of the applied voltage so that the outermost periphery is approximately shaped as a true circle. The driving frequency is set to the frequency that maximizes the amplitude of the fiber, i.e. the resonance frequency.